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I'm developing with CodeComposer 2.1 and dsk6711 a simple FFT
program with dsplib. This is the code: #include "DSPF_sp_bitrev_cplx" #include "ProvaFFTcfg.h" #define pi 3.14159265358979323846264338327950288419716939937510 #define FFT_SIZE 1024 #pragma DATA_MEM_BANK(PSD_W, 2); /* C62x and C67x have 16-bit banks */ #pragma DATA_ALIGN(PSD_Indeces,8) #pragma DATA_ALIGN(FFTBuffer,8) #pragma DATA_ALIGN(FFT_mag,8) #pragma DATA_ALIGN(FFT_Window,8) short PSD_Indeces[FFT_SIZE]; float FFTBuffer[FFT_SIZE*2]; float FFT_mag[FFT_SIZE/2]; float FFT_Window[FFT_SIZE]; float PSD_W[2 * 768] = { //} void CalcFFTMag(float * vect, int size, float * out) { int i; float I,Q; float alpha = 0.96043387; float beta = 0.397824735; // compute the fft magnitude for (i=0; i<size/2; i++){ I = fabs(vect[i*2]); //real Q = fabs(vect[i*2 +1]); //imag *(out+i) = (alpha*(MAX(I,Q)) + beta*(MIN(I,Q))); } } void main() { int i; for(i=0;i<FFT_SIZE;i++) FFT_Window[i] = 1.0 - powf((i - 0.5*FFT_SIZE)/(0.5*FFT_SIZE),2); for(i=0;i<FFT_SIZE;i++) { FFTBuffer[i*2] = cosf(2*pi*100*0.0005*i) * FFT_Window[i]; FFTBuffer[i*2 +1] = 0; } bitrev_index(PSD_Indeces,FFT_SIZE); DSPF_sp_cfftr4_dif(FFTBuffer,PSD_W, FFT_SIZE); DSPF_sp_bitrev_cplx((double*)FFTBuffer,PSD_Indeces, FFT_SIZE); CalcFFTMag(FFTBuffer,FFT_SIZE,FFT_mag); } But the application doesn't work well. Results are incorrect.... What's my fault? |
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dsplib problem!
Started by ●July 28, 2003
Reply by ●August 5, 20032003-08-05
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Results are correct upon return from DSPF_sp_cfftr4_dif(), the problem is that the correct results eventually are in incorrect order. That radix 4 FFT function leaves the output in the DIGIT-reversed order (where the digit is 4) and not in the bit-reversed order, like a radix 2 FFT routine would scramble it. On the contrary, the routines you've used to descramble the output perform the bit-reverse permutation: bitrev_index() and DSPF_sp_bitrev_cplx(), when digit-reverse permutation routines are in fact required. What's funny, the C67xx DSPLib does not have them :) One more bug. These routines are described and a source code is presented in SPRA440 Bit-Reverse and Digit-Reverse: Linear-Time Small Lookup Table Implementation for the TMS320C6000 Application Report, digitrev_index() and digitrev(). Hope this helps. Andrew Oops, I did not test the DSPF_sp_cfftr4_dif()! Might be buggy by itself :) Beware. On Mon, Jul 28 2003 "puffoinkazzato" <> wrote: > Date: Mon, 28 Jul 2003 08:24:24 -0000 > From: "puffoinkazzato" <> > Subject: dsplib problem! > > I'm developing with CodeComposer 2.1 and dsk6711 a simple FFT program > with dsplib. This is the code: > > #include "DSPF_sp_bitrev_cplx" > #include "ProvaFFTcfg.h" > > #define pi 3.14159265358979323846264338327950288419716939937510 > #define FFT_SIZE 1024 > > #pragma DATA_MEM_BANK(PSD_W, 2); /* C62x and C67x have 16-bit banks */ > #pragma DATA_ALIGN(PSD_Indeces,8) > #pragma DATA_ALIGN(FFTBuffer,8) > #pragma DATA_ALIGN(FFT_mag,8) > #pragma DATA_ALIGN(FFT_Window,8) > short PSD_Indeces[FFT_SIZE]; > float FFTBuffer[FFT_SIZE*2]; > float FFT_mag[FFT_SIZE/2]; > float FFT_Window[FFT_SIZE]; > float PSD_W[2 * 768] = { //} > > void CalcFFTMag(float * vect, int size, float * out) > { > int i; > float I,Q; > > float alpha = 0.96043387; > float beta = 0.397824735; > > // compute the fft magnitude > for (i=0; i<size/2; i++){ > I = fabs(vect[i*2]); //real > Q = fabs(vect[i*2 +1]); //imag > *(out+i) = (alpha*(MAX(I,Q)) + beta*(MIN(I,Q))); > } > } > > void main() > { > int i; > > for(i=0;i<FFT_SIZE;i++) > FFT_Window[i] = 1.0 - powf((i - 0.5*FFT_SIZE)/(0.5*FFT_SIZE),2); > > for(i=0;i<FFT_SIZE;i++) > { > FFTBuffer[i*2] = cosf(2*pi*100*0.0005*i) * FFT_Window[i]; > FFTBuffer[i*2 +1] = 0; > } > > bitrev_index(PSD_Indeces,FFT_SIZE); > > DSPF_sp_cfftr4_dif(FFTBuffer,PSD_W, FFT_SIZE); > DSPF_sp_bitrev_cplx((double*)FFTBuffer,PSD_Indeces, FFT_SIZE); > > CalcFFTMag(FFTBuffer,FFT_SIZE,FFT_mag); > } > > But the application doesn't work well. Results are incorrect.... > What's my fault? > |
Reply by ●August 5, 20032003-08-05
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You can get the DIGIT-reversal assembly code (call from C) from http://www-k.ext.ti.com/sc/technical-support/tools/dsp/ftp/c67x.htm I have used it and it works fine. Regards, Kurt Vetter -----Original Message----- From: Andrew Nesterov [mailto:] Sent: Monday, August 04, 2003 10:09 PM To: Subject: [c6x] Re: dsplib problem! Results are correct upon return from DSPF_sp_cfftr4_dif(), the problem is that the correct results eventually are in incorrect order. That radix 4 FFT function leaves the output in the DIGIT-reversed order (where the digit is 4) and not in the bit-reversed order, like a radix 2 FFT routine would scramble it. On the contrary, the routines you've used to descramble the output perform the bit-reverse permutation: bitrev_index() and DSPF_sp_bitrev_cplx(), when digit-reverse permutation routines are in fact required. What's funny, the C67xx DSPLib does not have them :) One more bug. These routines are described and a source code is presented in SPRA440 Bit-Reverse and Digit-Reverse: Linear-Time Small Lookup Table Implementation for the TMS320C6000 Application Report, digitrev_index() and digitrev(). Hope this helps. Andrew Oops, I did not test the DSPF_sp_cfftr4_dif()! Might be buggy by itself :) Beware. On Mon, Jul 28 2003 "puffoinkazzato" <> wrote: > Date: Mon, 28 Jul 2003 08:24:24 -0000 > From: "puffoinkazzato" <> > Subject: dsplib problem! > > I'm developing with CodeComposer 2.1 and dsk6711 a simple FFT program > with dsplib. This is the code: > > #include "DSPF_sp_bitrev_cplx" > #include "ProvaFFTcfg.h" > > #define pi 3.14159265358979323846264338327950288419716939937510 > #define FFT_SIZE 1024 > > #pragma DATA_MEM_BANK(PSD_W, 2); /* C62x and C67x have 16-bit banks */ > #pragma DATA_ALIGN(PSD_Indeces,8) > #pragma DATA_ALIGN(FFTBuffer,8) > #pragma DATA_ALIGN(FFT_mag,8) > #pragma DATA_ALIGN(FFT_Window,8) > short PSD_Indeces[FFT_SIZE]; > float FFTBuffer[FFT_SIZE*2]; > float FFT_mag[FFT_SIZE/2]; > float FFT_Window[FFT_SIZE]; > float PSD_W[2 * 768] = { //} > > void CalcFFTMag(float * vect, int size, float * out) > { > int i; > float I,Q; > > float alpha = 0.96043387; > float beta = 0.397824735; > > // compute the fft magnitude > for (i=0; i<size/2; i++){ > I = fabs(vect[i*2]); //real > Q = fabs(vect[i*2 +1]); //imag > *(out+i) = (alpha*(MAX(I,Q)) + beta*(MIN(I,Q))); > } > } > > void main() > { > int i; > > for(i=0;i<FFT_SIZE;i++) > FFT_Window[i] = 1.0 - powf((i - 0.5*FFT_SIZE)/(0.5*FFT_SIZE),2); > > for(i=0;i<FFT_SIZE;i++) > { > FFTBuffer[i*2] = cosf(2*pi*100*0.0005*i) * FFT_Window[i]; > FFTBuffer[i*2 +1] = 0; > } > > bitrev_index(PSD_Indeces,FFT_SIZE); > > DSPF_sp_cfftr4_dif(FFTBuffer,PSD_W, FFT_SIZE); > DSPF_sp_bitrev_cplx((double*)FFTBuffer,PSD_Indeces, FFT_SIZE); > > CalcFFTMag(FFTBuffer,FFT_SIZE,FFT_mag); > } > > But the application doesn't work well. Results are incorrect.... > What's my fault? > _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: Send an email to To Post: Send an email to To Leave: Send an email to Archives: http://www.yahoogroups.com/group/c6x Other Groups: http://www.dsprelated.com ">http://docs.yahoo.com/info/terms/ |
